This invention relates generally to antenna diversity systems, and more particularly, to antenna diversity systems for portable electronic devices.
Portable electronic devices such as handheld electronic devices are becoming increasingly popular. Examples of handheld devices include handheld computers, cellular telephones, media players, and hybrid devices that include the functionality of multiple devices of this type. Popular portable electronic devices that are somewhat larger than traditional handheld electronic devices include laptop computers and tablet computers.
Due in part to their mobile nature, portable electronic devices are often provided with wireless communications capabilities. For example, portable electronic devices may use long-range wireless communications to communicate with wireless base stations. Cellular telephones and other devices with cellular capabilities may communicate using cellular telephone bands at 850 MHz, 900 MHz, 1800 MHz, and 1900 MHz. Portable electronic devices may also use short-range wireless communications links. For example, portable electronic devices may communicate using the Wi-Fi® (IEEE 802.11) bands at 2.4 GHz and 5.0 GHz and the Bluetooth® band at 2.4 GHz. Data communications are also possible at 2100 MHz and the unlicensed 60 GHz band (57-66 GHz).
A number of compromises are typically made when designing antennas for a portable electronic device. For example, antennas that protrude excessively from a device housing may be unsightly. Antennas that are located within a device housing may be more desirable from an esthetic point of view, but can be challenging to design. Internal antennas are sometimes subject to proximity effects that make antenna performance dependent on the position of objects (such as a user's body) relative to the antenna.
Electronic devices that have redundant antennas (e.g., two or more antennas that operate in similar radio-frequency bands) may use diversity schemes to improve the reliability and performance of wireless communications activities. Traditional diversity schemes involve monitoring the strength or quality of signals that are received from multiple antennas in real time. If an antenna's performance drops below a given threshold, another antenna may be used for wireless communications activities. Antenna diversity schemes of this type may offer superior performance to arrangements that rely solely on a single antenna. However, waiting for antenna performance to degrade before making antenna adjustments can lead to undesirable dropped signals.
It would therefore be desirable to be able to provide improved antenna diversity systems.